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Krohn-Hite 522 DC calibrator.

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TimFox:
With respect to the tempco of the 1N829 reference zener:  one trick we  used in grad school was to measure a set of reasonable reference zeners in an oven at different current values.  Each individual zener would have 0 tempco at an idiosyncratic current value (while the catalog value was typically at 7.50 mA).

grumpydoc:

--- Quote from: TimFox on March 09, 2015, 02:25:04 pm ---With respect to the tempco of the 1N829 reference zener:  one trick we  used in grad school was to measure a set of reasonable reference zeners in an oven at different current values.  Each individual zener would have 0 tempco at an idiosyncratic current value (while the catalog value was typically at 7.50 mA).

--- End quote ---
I'm pretty certain that is what is done with all of the EDC voltage standards - if you look there is a small sticker on which is written a specific current/voltage so I think this is the zero tempco current for the diode.

NoisyBoy:
I know this is a very old topic, but has anyone cleaned the decade switches on the 522?  Mine is developing some poor connection inside the switches and sometimes needed some wiggle for it to settle on a digit.

nidlaX:

--- Quote from: NoisyBoy on March 03, 2020, 08:26:24 pm ---I know this is a very old topic, but has anyone cleaned the decade switches on the 522?  Mine is developing some poor connection inside the switches and sometimes needed some wiggle for it to settle on a digit.

--- End quote ---
Hey, funny you ask, I spent a Saturday doing this two weeks ago on my unit. I removed the entire front panel PCB from the chassis and did the following for each switch:

* Sprayed a bit of Deoxit Gold into each switch through the area around the shaft where there are holes (used a paper towel around the switch to reduce splash)
* Actuated the switch full-range about 20 times
* Sprayed compressed (canned) air into the switch the same way I sprayed the Deoxit (again wrapping with paper towel)
I can't say this is a permanent fix, but it did significantly improve switch contact and reduce bounce on my unit. That said, you could still have worn out switches on the most commonly used ranges depending on the age of your unit. If you need to, you might be able to find ITT Jeanrenaud switches new old stock on eBay or elsewhere.

Good luck!

NoisyBoy:
Excellent!  Thanks so much for the insight, instead of using the DeoxIT Gold spray, which has 0.5% cleaning action, I used DeoxIT D with 20% cleaning action.  It helped, but did not completely solved the problem, I can get everything to work, but I want it to work perfectly. 

So, I ordered 6 decade C&K RT-A switches tonight, hopefully that will allow me to completely refresh the calibrator.

Thanks for all your advice, otherwise I probably wouldn't have done anything with it.

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